The strange absence of lore for Shadow isn't Blizzard's fault, it's Shadows. You see, we're just so very cool - that we have banded together to restrict and contain all lore relating to how Shadowpriests come to be, and our role in the formation of universes. If the non-priests were ever made fully, or even partially, aware of our grandiose awesomeness - their feeble minds would explode via the neuro-chemical cocktail of unshackled envy, fathomless despair, and carnal lust.

It is a service and a penance we perform for the good of all Azeroth. A mere iota of our true lore shared publically would render the citizens of Azeroth immobile - stricken by sheer awe - to stand - gazing up into the inky night sky, ensorcelled by our magnificence, until they died of hunger where they stood. A sentence of our true purpose, if ever spoken a-loud, would bring this soulless universe into sentience, where in - in its primordial moment of consciousness - it would commit suicide rather than be left to know such greatness, but to know also that it would never be privy to know more than that first phrase of our ethos.

Be greatful, now-humbled citizen of Azeroth!

For though I cannot share with you even a word - stricken of context - of our illustrious history, you must have faith that we Shadowpriests are borne of a purpose more elegant, more rapturous, than your mind can comprehend. Be humble in our company, and like a graceful swan - we may deign to offer you our glorious presence - that you might bathe in the radiance of lights' absence!

Those that follow only the light will avoid the darkness and see it only as a source of death and despair.
Those that follow only the darkness embrace it, allow it to control them, and are ultimately destroyed by it.
But the true shadow priest is one that can cause both light and dark to function in perfect harmony as a singular weapon of justice.

There aren't many warlocks in the lore either; and when they are, they're usually bad guys or idiots (read: Fizzlebang). There was one scene in Throne of the Tides where Garrosh fights a Felguard that a warlock summons, but I really haven't seen many warlocks in lore. I think the problem is that player classes don't really show up in the lore as their own thing, and it's usually about the characters.

What we need is a major lore character that is also a shadow priest, like a Forsaken or a renegade Draenei.

Edit: Or, maybe Anduin will become a shadow priest after his recent brush with death.

"So my advice is to argue based on the reasons stated, not try to make up or guess at reasons and argue those."
Greg Street, Riot Developer - 12:50 PM - 25 May 2015

You see, I find this lack of real lore inspiring for my character. We know the only official shadow priests are the Forsaken ones. But that can easily be extended to other races via something very simple: Curiosity.

- Coming across an old book about shadow magic in that "forbidden library".
- Meeting an undead willing to teach you the other side of the Light.
- Or just being unfit for the Light and finding out a better way to help others by destroying their enemies instead of healing their wounds.

I don't think any more races need a shadow cult. In fact, I'd say shadow priests are more about individuals. Angry, vengeful and twisted individuals.

I'd like to see shadow priests as watchers of the night/dark.
Someone needs to watch the shadow because even the smallest of creatures can cast the largest shadows.
Because when darkness/night falls, the light can never shine bright enough and that is where shadow priests jump in. Whether good or evil, we exist and don't exist. The shadow is just an illusion, a cast of emptiness.

"Night gathers, and now my watch begins. It shall not end until my death. I shall wear no crowns and win no glory. I shall live and die in the night. I am the sword in the darkness. I am the watcher in the shadows. I am the shadow of the fires, the dark that brings the dusk, the horn that gathers the sleepers, the shield that guards the sleeping realm. I pledge my life and honor to the shadow, for this night and all nights to come."

So I started a shadow priest and had to check the web if there's any kind of info on what Shadow Priest actually are in lore. I found almost no answers, granted there's Cult of the Forgotten Shadows, but that is lacking, just doesn't seem to be as big as Shadow Priest lore could be.

Now I was thinking, first option is obviously the Orc Necrolytes, type of Necromancers, just not as profound as let's say Death Knights later on, but still Necromancers.

The second option could be Cult of the Damned Acolytes, who were basically priests that dabbled in dark magic, still not as "magical" as Necromancers or Liches, who were essentially Mages that have gone dark.

Now the third option could also be Twilight Hammer, as we all know, after Cho'gall's defeated it was Archbishop Benedictus himself who was active in working with/for the old gods.

It's an interesting topic, and they all have roots in Orcs Necrolytes yet Orcs can't be Priests :P

Much like in World of Warcraft, Thread Necromancy is a forbidden art on the MMO-C forums ;p